1. Field of the Invention
The present invention relates to an electrical apparatus winding for a transformer, reactor or a superconductive magnet, and more particularly to an electrical apparatus winding wound in disk shape or helical shape to improve cooling effect.
2. Description of the Prior Art
FIG. 1 is a schematic sectional view illustrating an example of a prior art disk-shaped winding for an electrical apparatus such as a transformer and FIG. 2 is a sectional view taken along a line II--II in FIG. 1. As shown in FIGS. 1 and 2, the transformer winding usually comprises a plurality of winding units 5 each composed of a wire element 4 are serially arranged vertically between an inner insulating sleeve 2 and an outer insulating sleeve 3 which are arranged concentrically around an outer circumference of a core 1. Formed between adjacent winding units 5 are horizontally extending cooling paths (hereinafter referred to as horizontal cooling paths) 6 by horizontal duct pieces (not shown), and formed between each of the winding units 5 and the inner insulating sleeve 2 and between each of the winding units 5 and the outer insulating sleeve 3 are inner and outer vertically extending cooling paths (hereinafter referred to as vertical cooling paths) 7 and 8, respectively, by vertically extending linear duct pieces (not shown).
With the cooling paths thus constructed, however, cooling fluid flows as shown by arrows 9 and 10 as the winding units 5 are heated with the result that the flow in the horizontal cooling paths 6 is very slow. As a result, the temperature at the center of each of the winding units 5 rises and may overheat the winding. In order to prevent such overheating, the horizontal cooling paths 6 must be designed larger. This results in the increase of size of the entire winding. FIGS. 3 to 5 show schematic sectional views illustrating other examples of prior art electrical apparatus windings, such as disk-shaped windings for a transformer. The winding structure of FIG. 3 is shown in Japanese Utility Model Application No. 48-50916 (Published Unexamined Utility Model Application No. 49-150303), in which each of the winding units 5 shown in FIGS. 1 and 2 is divided into a plurality of (two in the example shown in FIG. 3) winding sub-units 5a and 5b to define a central vertical cooling path 11 therebetween, with the remaining portions being identical to the winding structure shown in FIGS. 1 and 2. With this winding structure, temperature at the center of each of the winding units 5 is lowered by the cooling fluid flowing through the central vertical cooling path 11 but the flow of the cooling fluid in the horizontal cooling paths 6a and 6b defined between the winding sub-units 5a and between the winding sub-units 5b, respectively, is still very slow like in the case of FIG. 1. Accordingly, the temperature at the center of each of the winding sub-units 5a and 5b still rises. In order to prevent such temperature rise, the winding sub-units 5a and 5b may be further divided, but in this case the size of the winding unit 5 increases by a length corresponding to the total width of additional central vertical cooling paths. In addition, the structure of the winding is very much complicated. An alternative approach for the winding structure is shown in FIG. 4 which is disclosed in the Japanese Utility Model Application No. 48-126273 (Published Unexamined Utility Model Application No. 50-69616), in which each of the winding units 5 is divided into a plurality of (two in the example shown in FIG. 4) winding sub-units 5c and 5d to define a zig-zag vertical cooling path 12 between the winding sub-units 5c and the winding sub-units 5d, with the remaining portions being identical to the winding structure shown in FIGS. 1 and 2. With the cooling path thus constructed, the cooling fluid having passed through the vertical cooling path 12 in one stage collides against the wider winding sub-unit 5d of the next stage winding sub-units 5c and 5d disposed above said one stage and is divided into horizontal cooling paths 6c and 6d. However, when the flow rate of the cooling fluid is slow as a whole, the flow rate of the cooling fluid passing through the vertical cooling path 12 is as slow as the flow rate of the cooling fluid passing through the horizontal cooling paths so that the flow rate of the cooling fluid flowing through the horizontal cooling paths 6c is lower than the flow rate of the cooling fluid passing through the horizontal cooling paths 6d. As a result, the flow stagnates at the horizontal cooling paths 6c under the narrower winding sub-units 5c, as shown by arrows in FIG. 4 or the flow is slow and unstable at those regions. As a result, the temperature of those portions of the winding which face those regions rises. In order to prevent such temperature rise, the size of the cooling paths must be increased, but this leads to the increase of size of the entire winding. As another approach, a winding structure shown in FIG. 5 is proposed, which is disclosed in the Japanese Utility Model Application No. 28-33702 (Published Examined Utility Application No. 30-5533), in which the entire side surface of the laminated winding units 5 is enclosed by an insulator 13 and each of the winding units 5 is divided into sub-units with a wider spacing 14 and a narrower spacing 15 therebetween, which alternate from winding unit to winding unit, with the remaining portions being identical to the winding structure shown in FIGS. 1 and 2. With the cooling path thus constructed, by virtue of the arrangement of the spacings 14 and 15 the flow of the cooling fluid is divided into flows which pass only along the sides of the winding units 5 and the flows which pass along the upper and lower surfaces of the winding units 5. The cooling fluid flows in the horizontal cooling paths 6e at the center portions of the winding units 5 but does not flow in the horizontal cooling paths 6f which are encircled by the end portions of the winding units 5 and the insulator 13 and creates eddies. As a result, the winding portions facing those regions may be unduly heated. In order to prevent such heating, the size of the cooling path must be increased but this leads to the increase of the size of the entire winding.